Blends of polyamides with polycarbonates, poly(ester carbonates) and polyarylates are known to exhibit desirable properties including excellent solvent resistance, ductility, hydrolytic stability and resistance to brittle failure when molded into articles. See, for example, the copending, commonly assigned U.S. patent application of L. M. Maresca, D. C. Clagett and U. S. Wascher, Ser. No. 812,433 filed Dec. 23, 1985 now abandoned, and U.S. Pat. No. 4,798,874, which is a continuation-in-part of Ser. No. 07/812,433. Novel polyamide-polyarylate copolymers have been prepared which have excellent and improved physical and mechanical properties, and good chemical resistance and barrier properties, and these are the subject matter of commonly assigned copending application Ser. No. 07/117,250, now abandoned. Such copolymers are prepared in a melt polymerization process. The microstructure of the polymer can be controlled by running the process in one or two steps. A wide variety of diamines, diphenols and diacid esters can be used in the process in both steps. If, for example, a polyamide polyarylate block copolymer is desired, a two step process is used. In the first step, for example, diphenyl iso/terephthalate is reacted with a diamine in the melt at, for example, 120.degree. C.-280.degree. C., to produce amide units. If a diphenol such as bisphenol-A and diphenyl iso/terephthalate is added in a second step and the temperature of 230.degree. C.-320.degree. C. is used arlyate units will then be smoothly produced at reduced pressures as byproduct phenol is removed. Although Fox and Shafer, U.S. Pat. No. 4,567,249, disclose the melt preparation of polyamides by amine-ester interchange, there is no hint of suggestion in that patent to employ the process employing both an amine on the one hand, and a dihydric phenol on the other. It has now been found that amide-ester copolymers, including random copolymers, block copolymers and alternating copolymers, can be synthesized by a melt polymerization process. If carried out stepwise, in one step a polyamide block can be formed by the reaction of a diamine with a diaryl ester, e.g., diphenyl iso/terephthalate at temperatures ranging from about 120.degree. C. to about 280.degree. C. In a second step, a diol such as ethylene glycol, or 1,4-butanediol can be used in the reaction along with diacid ester to form the polyester at similar temperatures i.e., more moderate than required to make the polyarylate blocks. The new materials, which can be made from a wide variety of diamines, diols and diacid esters, have excellent mechanical and physical properties good chemical resistance and barrier properties.